1. Field of the Invention
The present invention relates generally to multi-layer substrates suitable for electronics applications, such as, bonding films to form multi-layer flexible circuits, rigid-flex circuits, chip scale packaging, wafer scale packaging or the like. More specifically the multi-layer substrates of the present invention comprise a metal layer, an aliphatic/aromatic polyimide layer and an aromatic polyimide layer, combined in a way to provide advantageous strength and (z-axis) coefficient of thermal expansion properties.
2. Discussion of Related Art
U.S. Pat. No. 5,922,167 to Rosenfeld is directed to polyimide adhesive compositions, having bonding temperatures taught to be in a range of about 250° C. to 450° C.
The present invention relates to prior research disclosed in U.S. Pat. No. 5,298,331, to Kanakarajan, et al. for polyimide adhesives with bonding temperatures in a range of about 250° C. to 275° C. The methods of manufacture and use described in the Kanakarajan patent are also applicable to the polyimide adhesives of the present invention, and therefore the Kanakarajan et al. patent is hereby incorporated by reference into this specification for all teachings therein.